1. Technical Field
The present invention relates to a separation method intended to extract a target, using viscosity of a liquid, from a separation subject in which the target and a non-target are mixed.
2. Description of the Related Art
In recent years, economic activities represented by mass production, mass consumption, and mass disposal have caused environmental problems on a global scale, such as global warming and depletion of resources. Under such circumstance, in Japan, Home Appliance Recycling Law, which came into effect in April 2001, obliges recycling of used air conditioners, televisions, refrigerators/freezers, and washing machines, to build a recycling society.
Conventionally, unneeded home appliances have been recycled by crushing and then separating them by material, using magnetism, wind, oscillation, etc., in home appliance-recycling plants. The recycling rate of heavy metal materials used for home appliances is high because the use of a specific-gravity separation device or a magnetism separation device allows these materials to be separated by material such as iron, copper, aluminum, etc., and thus recovered in very pure form.
Resin components in home appliances may be separated using water. For example, a resin component of polypropylene (hereinafter denoted as PP), which has a low specific gravity, is separated from a component having a high specific gravity through specific gravity segregation using water and thus recovered with a relatively high degree of purity. This separation method using water, however, has a problem that an enormous amount of wastewater is produced, and further has a significant problem that polystyrene (hereinafter denoted as PS) and acrylonitrile-butadiene-styrene (hereinafter denoted as ABS), which have close specific gravities, are not separated from each other.
In addition, with concern for depletion of rare metals, the development of technology for recovering rare metals from precision equipment and the like has become an issue.
Particularly, as to the recycling of resin components, separation methods in consideration of the above problems have been proposed in Japanese Unexamined Patent Application Publication No. 2002-234031 and Japanese Unexamined Patent Application Publication No. 2000-108126.
JP 2002-234031 discloses a method of separating resin components that are different in constituent resin substance. The method uses a difference in dielectric loss between the resin components. In this method, a separation subject having resin components of two or more resin kinds is subjected to dielectric heating using electromagnetic waves or the like so that the resin components, which are molten differently from each other, are separated from each other.
JP 2000-108126 discloses a method of separating resin constituents which uses near infrared rays to detect a difference in peak wavelength between the resin materials. In this method, resin components of a desired resin kind are separated from a separation subject in such a manner that resin kinds of constituent substances are specified using a resin property that constituent resin substances of different kinds have different wavelength peak positions in a near infrared region, and according to the specified resin kinds, only resin components of a predetermined resin kind are blown off by means of an air nozzle or the like. It is highly likely that a group of the separated resin components is made of resin substances, which are the same in kind, resulting in a higher degree of purity.
These separation methods produce no wastewater and are not influenced by the specific gravity of a resin component.